3916
Ind. Eng. Chem. Res. 2006, 45, 3916-3921
Experimental Study on the Adsorption of Water and Ethanol by Cornmeal for Ethanol Dehydration Hua Chang, Xi-Gang Yuan,* Hua Tian, and Ai-Wu Zeng State Key Laboratory of Chemical Engineering, Chemical Engineering Research Center, School of Chemical Engineering and Technology, Tianjin UniVersity, Tianjin 300072, China
A fixed-bed apparatus was designed to investigate the gas adsorption capacity and selectivity of cornmeal for ethanol dehydration. The experiments were performed at near atmospheric pressure and at different temperatures and different ethanol vapor concentrations. Both equilibrium and kinetic adsorptions at the breakthrough point were conducted. The effects of superficial velocity, temperature, and vapor feed concentration on the adsorption capability were studied. The experimental results show that the water selectivity over ethanol on cornmeal is on the order of 0.5-0.6 for both equilibrium and kinetic conditions at the breakthrough point, the equilibrium adsorption capacity for cornmeal is 2.9 g of water/100 g of adsorbent and 2.5 g of ethanol/ 100 g of adsorbent under the conditions of 91 °C and 93.8 wt % ethanol vapor feed concentration, and the kinetic selectivity of water over ethanol at the breakthrough point is slightly higher than the equilibrium value. The adsorption isotherm for water was correlated as a linear expression for ethanol vapor feed concentrations of 85.0-95.2 wt % The experimental results demonstrate that the likelihood of selective adsorption can be given by the dynamic behavior of the adsorption of water and ethanol on cornmeal. 1. Introduction
Table 1. Particle Size Distribution of Cornmeal
The separation of ethanol-water mixtures for the production of pure ethanol is usually divided into two steps. From 10 to 92 wt % ethanol, distillation is effective. Above 92 wt %, as the azeotropic point at 95.57 wt % ethanol is approached, distillation becomes costly, and alternative processes must be applied.1 Azeotropic distillation, salt extractive distillation, and molecular sieve adsorption have been employed for this purpose. Biomass adsorption is known as an energy-saving and promising alternative for the second stage of ethanol dehydration.2,3 A number of investigations of biomass adsorption have been made.1,3-11 Ladisch and Dyck first demonstrated that biomass, including starch and cellulose, can be used as an adsorbent to selectively adsorb water to give an ethanol product of more than 99.5 wt % purity. Generally, the dilute solution is concentrated to 85-92 wt % ethanol, and then the biomass adsorbents can be used to adsorb water in the vapor phase to obtain an ethanol product of 99.5 wt %. The saturated adsorbent can be used directly as fermentation material without being regenerated, leading to further reductions of energy consumption.1,4-5 However, few data have been reported in the open literature on biomass adsorption behavior for the binary ethanol-water vapor system, and there is no consistent conclusion on the adsorptive capacity for ethanol. Some workers have suggested that almost no ethanol is adsorbed,5-8 whereas some others have proposed that significant ethanol is adsorbed.9-11 Some works conducted on starch adsorption for both water and ethanol using nitrogen as the carrier gas have been reported.11 Preliminary bench-scale works on biomass selective adsorption for the water-ethanol binary system have also been reported.10 Aimed at practical applications, this article investigates, on the pilot scale, the adsorption capacity and selectivity of biomass adsorbent in the binary ethanol-water vapor system under different operating conditions including different temperatures and different concentrations of vapor feed . For practical * To whom correspondence should be addressed. Tel.: +86 22 27404732. Fax: +86 22 27404496. E-mail:
[email protected].
particle size (mm)
fraction of particles (%)
